Today blood collection organizations routinely separate whole blood into its various therapeutic components, such as red blood cells, platelets, and plasma.
One separation technique that is in widespread use today uses a multiple blood bag system. The bag system includes a primary blood bag and one or more transfer bags, which are integrally connected to the primary bag by tubing. The technique collects from a donor a single unit (about 450 ml) of whole blood in the primary blood bag. The donor is then free to leave.
The donor's whole blood later undergoes centrifugal separation within the primary bag into red blood cells and plasma rich in platelets. The plasma rich in platelets is expressed out of the primary bag into a transfer bag, leaving the red blood cells behind. The plasma rich in platelets then undergoes further centrifugal separation within the transfer bag into a concentration of platelets and plasma poor in platelets. The plasma poor in platelets is expressed from the transfer bag into another transfer bag, leaving the concentration of platelets behind.
Using multiple blood bag systems, all three major components of whole blood can be collected for therapeutic use. However, the yield, for each component collected is limited to the volume of the components that are contained in a single unit of whole blood. Furthermore, because red blood cells are retained, United States governmental regulations prohibit collecting another unit of whole blood from the donor until six weeks later.
Certain therapies transfuse large volumes of a single blood component. For example, some patients undergoing chemotherapy require the transfusion of large numbers of platelets on a routine basis. Multiple blood bag systems simply are not an efficient way to collect these large numbers of platelets from individual donors.
On line blood separation systems are today used to collect large numbers of platelets to meet this demand. On line systems perform the separation steps necessary to separate a concentration of platelets from whole blood in a sequential process with the donor present. On line systems establish a flow of whole blood from the donor, separate out the desired platelets from the flow, and return the remaining red blood cells and plasma to the donor, all in a sequential flow loop.
Large volumes of whole blood (for example, 2.0 liters) can be processed using an on line system. Due to the large processing volumes, large yields of concentrated platelets (for example, 4.times.10.sup.11 platelets suspended in 200 ml of fluid) can be collected. Moreover, since the donor's red blood cells are returned, the donor can donate whole blood for on line processing much more frequently than donors for processing in multiple blood bag systems.
Regardless of the separation technique used, when collecting blood components for transfusion, it is desirable to minimize the presence of impurities or other materials that may cause undesired side effects in the recipient. For example, because of possible febrile reactions, it is generally considered desirable to transfuse red blood cells and platelets that are substantially free of leukocytes, particularly for recipients who undergo frequent transfusions.
Several United States Patents are directed to the removal of leukocytes from red blood cells and platelet components in multiple blood bag systems. For example, see U.S. Pat. Nos. 4,767,541; 5,089,146; 5,100,564; and 5,128,048.
Nevertheless, a need still exists for further improved systems and methods for removing undesired matter like leukocytes from blood components in a way that lends itself to Use in high volume, on line blood collection environments, where higher yields of critically needed blood components like platelets can be realized.